1. Field of the Invention
This invention relates to a data reproducing apparatus and more particularly, is applicable to a data reproducing apparatus having a rotary head and a control head.
2. Description of the Related Art
Heretofore, a data recorder conformed to the ANSI ID-1 format (Third Draft PROPOSED AMERICAN NATIONAL STANDARD 19 mm TYPE ID-1 INSTRUMENTATION DIGITAL CASSETTE FORMAT X386/88-12 project 592-D 1988-03-22) has been provided as a recording/reproducing apparatus for high density recording of information data.
In these data recorders, an error correction coding with product coding format is conducted by using Reed-Solomon code on the information data and these are recorded on the magnetic tape, and transmission errors are detected and corrected at the time of reproduction.
As shown in FIG. 1, this data recorder 1 winds a magnetic tape 3 around a rotary drum 2 which is rotating with the prescribed speed in the direction of an arrow "A" by a capstan 4, and as shown in FIGS. 2A and 2B, recording tracks composed of ID-1 format are formed by rotary heads loaded on the rotary drum 2 and a control head 5. An example of the data recorder is disclosed in the U.S. Pat. No. 5,185,740 which is assigned to the assignee of the present application.
More specifically, in the data recorder 1, annotation track ANN to be recorded with annotation information, control track CTL to be recorded with recording information and time code track TC to be recorded with time code information are formed in the longitudinal direction on the upper and lower ends of the magnetic tape 3 by the control head 5 and simultaneously information data is recorded helically on the magnetic tape 3 by the rotating head loaded on the rotary drum 2 and data tracks TR0, TR1, TR2, TR3, TR0, TR1, . . . are formed.
In this event, the data tracks TR are arranged to compose track sets T.sub.N-1, T.sub.N, . . . every four data tracks TR0, TR1, TR2, TR3, and track set discrimination information to discriminate track sets T.sub.N-1, T.sub.N, . . . are recorded on each data track TR0, TR1, TR2, TR3, and control track CTL. Each data track TR0, TR1, TR2, . . . is azimuth recorded alternately and simultaneously one sector per one track is formed.
At this point, each track TR0, TR1, TR2, . . . , as shown in FIG. 3A, is comprised of a preamble unit PR, a data recording unit DT and a post recording or postamble unit PS composed of 256 synchronizing blocks BLK.sub.0 to BLK.sub.255, which are arranged from the lower front part to the upper front part of the magnetic tape 3 successively in that order.
As shown in FIG. 3B, in the preamble unit PR, an undefined area UND where data to be written in is not defined, 180 bit length rising sequence RUS, 36 bit length synchronizing code SYNC.sub.PR, 36 bit length data track discrimination data ID.sub.DATAl and 54 bit length auxiliary data DT.sub.AUX are arranged successively in that order, and as shown in FIG. 3C, 2 bit track number information ID.sub.TR which shows each track number TR0, TR1, TR2, TR3, in each track set and 22 bit track set number information ID.sub.SET1 which shows the number of track sets T.sub.N-1, T.sub.N, . . . are recorded in the track discrimination data ID.sub.DATA1.
With this arrangement, in the data recorder 1, phase information of the rotary drum 2 can be obtained by reading out the synchronizing code SYNC.sub.PR, and simultaneously track sets T.sub.N-1, T.sub.N, . . . of data tracks whereon the rotary head is scanning and track numbers TR0, TR1, TR2, and TR3 can be detected by reading out the track set number information ID.sub.SET1 and the track number information ID.sub.TR,
Furthermore, in each synchronizing block BLK.sub.0 to BLK.sub.255 of sequential data recording unit DT, 36 bit length synchronizing code SYNC.sub.BLK, 9 bit length block discrimination data ID.sub.BLK, 153.times.9 bit length inner data DI and parity code RI composed of 72 bit length Reed Solomon code are successively arranged in that order.
Moreover, in the postamble unit PS, 36 bit length synchronizing code SYNC.sub.PS and data track discrimination data ID.sub.DATA2 are successively arranged.
At this point, as shown in FIG. 4, recording system 1A of the data recorder 1 conducts an error coding of product coding format on the input information data and records this on the magnetic tape 3.
More specifically, in the data recorder 1, input information data DT.sub.USE which is composed of 8 bits per 1 byte is inputted to an outer code formation circuit 10. The outer code formation circuit 10 forms a parity code composed of 10 bytes of Reed Solomon code as an outer code in utilizing the prescribed formation polynomial and adds this at the end of the input information data DT.sub.USE and outputs to a memory 12 via a first multiplexer 11 as an outer data block DO.
Moreover, in the memory 12, data block discrimination data ID.sub.B generated at the discrimination data generation circuit 13 for discriminating each line of the memory 12 is sent via the first multiplexer 11 and the data written in the memory 12 are read out in accordance with the order of data block discrimination data ID.sub.B.
The data read out from the memory 12 is outputted to an inner code formation circuit 14. The inner code formation circuit 14 forms the parity code composed of 8 bytes of Reed Solomon on each data block to be inputted as the inner code in utilizing the prescribed formation polynomial and adds the parity code to the tail of each data block and outputs to the second multiplexer 15 as an inner data block DI.
The second multiplexer 15 successively selects the preamble data PR and the postamble data PS which are formed at the preamble/postamble generation circuit 16 and the inner data block DI composed of the output of the inner code formation circuit 14, and outputs these to a data randomizing circuit 17 in the order of preamble data PR, inner data block DI and postamble data PS.
The data randomizing circuit 17 randomizes data by taking the exclusive OR with the prescribed data on each 1 byte of the data inputted and outputs the randomized data an 8-9 modulation circuit 18.
The 8-9 modulation circuit 18 converts the data composition from 8 bit to 9 bit in order to eliminate the direct current element of a signal waveform to be recorded on the magnetic tape 3. An example of the 8-9 conversion is disclosed in the U.S. Pat. No. 5,192,949 which is assigned to the assignee of the present application.
This conversion is summarized as follows:
More specifically, two kinds of 9 bit data are defined in advance by an ID-1 format regarding each value of 1-byte 8-bit input data having 256 kinds of value. These two kinds of 9 bit data are data having opposite polarity, positive and negative, of CDS (Codeword Digital Sum), and the 8-9 modulation circuit 18 watches DSV (Digital Sum Variation) of 9 bit data to be outputted corresponding to the input data and selects one of two kinds of 9 bit data having different CDS values in order that the value becomes zero. With this arrangement, the 8-9 modulation circuit 18 converts the input data composed of 1 byte 8-bit to the data of DC free 9 bit data. Also, the 8-9 modulation circuit 18 has a circuit which converts the format of input data of NRZL (Nonreturn to Zero Level) to NRZI (Nonreturn to Zero Inverse).
The output the 8-9 modulation circuit 18, i.e., the data composed of 9 bit NRZI is inputted to the third multiplexer 19. This multiplexer 19 forms synchronizing blocks BLK.sub.0 to BLK.sub.255 adding 4 byte length fixed synchronizing codes SYNC.sub.B to be formed in the synchronizing code generation circuit 20 for each data block of the inner data block DI. The code pattern of this synchronizing code SYNC.sub.B is defined by the ID-1 format and it is also defined that the pattern to be recorded on the magnetic tape 3 must hold the format of this code pattern.
The output the third multiplexer 19 is inputted to parallel serial converter 21 which converts each data of the bit parallel composed preamble unit PR, synchronizing blocks BLK.sub.0 to BLK.sub.255 and postamble unit PS to be inputted to the bit serial composed data S.sub.REC.
This serial data S.sub.REC, after being amplified at the recording amplifier 22, is supplied to the magnetic head 24 which is helically scanning the magnetic tape 3 for a recording signal and thus, the data tracks TR (. . . , TR0, TR1, TR2, TR3, . . . ) are formed on the magnetic tape 3 as shown in FIGS. 2A and 2B. With this arrangement, recording system 1A of the data recorder 1 is able to record the desired information data DT.sub.USE by adding error correction codes in conformity with a Reed Solomon product coding format.
Furthermore, the information data DT.sub.USE recorded on the magnetic tape 3 by the recording system 1A of the data recorder 1 is reproduced in the reproducing system 1B of the data recorder 1 as shown in FIG. 5.
The reproducing system 1B is arranged to perform the signal processing which is completely contrary that performed by the recording system 1A. More specifically, the reproducing system 1B of the data recorder 1 reads out recording information recorded on the data tracks TR (. . . , TR0, TR1, TR2, TR3, . . . ) on the magnetic tape 3 as reproducing signal S.sub.PB in utilizing the magnetic head 24 and outputs this to a reproducing amplifier 25.
The reproducing amplifier 25 comprises an equalizer and a binary coding circuit, and performs binary coding on the reproducing signal S.sub.PB inputted and outputs to the following serial/parallel converter 26 as reproducing digital data DT.sub.PB. This serial/parallel converter 26 converts serial format reproducing digital data DT.sub.PB to 9 bit parallel data DT.sub.PR and outputs this to synchronizing code detection circuit 27.
The synchronizing code detection circuit 27 detects synchronizing codes SYNC.sub.B from a flow of parallel data and discriminates synchronizing codes based on this. Also, the synchronizing code-detection circuit 27 converts NRZI format parallel data DT.sub.PR to the NRZL format.
An output of the synchronizing code detection circuit 27 is inputted to the 8-9 demodulator 28. The 8-9 demodulator 28 is composed of ROM (Read Only Memory) and after demodulating the data converted from 8 bit to 9 bit for DC randomizing in the recording system 1A from 9 bit to 8 bit in utilizing the conversion table, outputs to data derandomizing circuit 29.
The data derandomizing circuit 29 derandomizes the restored data by performing an exclusive OR calculation processing in conformity with the data restored to 8 bit and the same fixed data used in randomization at the time of recording.
An inner code error detection correction circuit 30 performs error detection and correction on the inner data block in synchronizing blocks discriminated at the synchronizing code detection circuit 27 in utilizing the 8 byte length inner code added to each block.
Inner data blocks that have received inner code error correction are written in a memory 32 having the same composition as the memory 12 (FIG. 4) of the recording system 1A, based on the block discrimination data ID.sub.B added to each block to be detected by the discrimination data detection circuit 31 as one data block per one line. The writing-in order is the same as those of the reading out order of the recording system 1A of the memory 12.
The data written in the memory 32 is read out by the outer code error detection correction circuit 33 in a similar order to the writing-in order of the recording system 1A and as a result, the outer data block DO can be obtained again. The outer code detection correction circuit 33 performs error detection and correction on the outer data blocks in utilizing the outer code added to each block. Thus, the information data DT.sub.USE recorded on the magnetic: tape 3 can be reproduced.
In this data recorder 1, as described above in FIGS. 1, 2A and 2B, track sets T.sub.N-1, T.sub.N, . . . composed of data tracks TR0, TR1, TR2, and TR3 are formed in a longitudinal direction helically on the magnetic tape 3 by a plurality of rotary heads loaded on the rotary drum 2 and simultaneously control track CTL is formed in a longitudinal direction of the magnetic tape 3 by the control head 5, and the same track set number information ID.sub.SET2 as the track set number information ID.sub.SET1 (FIGS. 3A to 3C) recorded on the data tracks TR is recorded on the control track CTL.
With this arrangement, in the data recorder 1, the rotary head loaded on the rotary drum 2 can trace on the data tracks TR wherein the track set number information ID.sub.SET1 is written in corresponding to the above track set number information ID.sub.SET2 since the control head 5 reads out the track set number information ID.sub.SET2 on the control track CTL at the time of fast forwarding or rewinding.
At this point, in the data recorder 1, the track set number information IDSET2 on the control track CTL is recorded on the same position as those of track sets T.sub.N-1, T.sub.N, . . . on the corresponding data tracks TR in a longitudinal direction of the tape by recording the track set information ID.sub.SET2 delayed for the distance difference between the standard point of writing-in and reading-out of the rotary head and the standard point of write-in and read-out of the control head 5 for the track set number information ID.sub.SET1 on the corresponding data tracks TR.
However, as shown in FIG. 1 in the data recorder 1, there are cases where the position of control head 5 shifts in the direction of B, farther from the rotary drum 2, or closer to the rotary drum 2 in the direction of C.
At this point, in the data recorder 1, in the case where the position of control head 5 shifts for integral multiples of the data track (in the case of an azimuth recording system where it shifts for even number multiples of the data track) since the shift cannot be detected, there has been a problem that recording which does not agree with the format has been conducted.
Therefore, in the conventional data recorder 1, the control head 5 is arranged at the correct position and simultaneously, a method to adjust the phase of the rotary drum has been used by conducting various adjustments such as RF envelope adjustment, position adjustment of the control head and phase adjustment of the drum, observing the RF signal obtained at the time when the above standard tape is reproduced with oscilloscopes, on the basis of a servo reference signal in utilizing an exclusive standard tape at the time of manufacture.
However, in this method it is necessary to have measuring devices such as special standard tapes and oscilloscopes, as well as professional knowledge. Therefore, in practice it was impossible that the user could conduct these adjustments directly.